I built a large quarry and as it was getting closer to the ground I dug a hole with a ladder in it to get down to the bottom, but as I was down on the bottom I noticed that I could see the quarry arm cross-arms at the top, but they were standing still.

I could not determine if the arm was still moving as the whole thing was flooded, but from down at the bottom of that ladder, the arms were still.

As I climbed back up, they started moving again.

Was this:

Just a distance-thing sight-wise, that the game did not update what my client was viewing as the machines was so far away (70 blocks above me)

A distance-thing operation-wise, and the machine really did stop as I got too far away from it

I ask because now that the whole quarry is done, and I have emptied it for water, I planned on building a completely automated storage facility in it, and I was planning on placing the sorting machines and processing (smelting, etc.) at the bottom, but if that means that those things will not operate unless I'm a bit down into my structure, that may not be a good idea.

OK, guess I'll have to experiment a bit then, perhaps if I built a item teleporter pipes and let them come out at the botton, then I would easily see if machines at the surface-level worked when I was at bedrock-level.
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Lasse V. KarlsenAug 22 '12 at 6:56